In a railroad vehicle, an air spring is arranged between a vehicle main body and a bogie to reduce the impact and vibration applied to the vehicle body while the vehicle is running. The air spring mainly includes an upper surface plate connected to the vehicle main body side, a lower surface plate arranged below the upper surface plate, and a rubber diaphragm arranged to connect the upper surface plate and the lower surface plate, and by elastic deformation of the diaphragm, the air spring can reduce the impact and vibration in the vertical direction during running. Examples of a sealing method for ensuring the air tightness of the diaphragm in the air spring include a fastening sealing method in which the diaphragm is sandwiched between the upper surface plate and one fastening fitting as well as between the lower surface plate and the other fastening fitting, and the diaphragm is fastened by bolts (refer to, for example, Miyamoto, “Illustrated Description of Mechanism of Train-Thorough Elucidation of Commuter Train-”, 2nd edition, Toyokuni Printing Co., Ltd., January, 2010, p. 46 (NPD 1)), a self-sealing method in which the diaphragm is fixed to each of the upper surface plate and the lower surface plate by using the inner pressure of the diaphragm (refer to, for example, “Spring Rigging for Railway Rolling Stock JISE 4206”, Japanese Industrial Standards Committee, May, 1989, p. 8, 10-12 (NPD 2)), and the like.